1. Field of the Invention
The present invention relates generally to an apparatus and method for charging a power source and, more specifically, to an apparatus and method for simultaneously or sequentially charging a power source and providing electric energy to a lighting or lamp system.
2. Description of the Prior Art
In recent years, the use of solar energy and wind energy has become an increasingly important source of energy and the availability and efficiency of photovoltaic cells and photovoltaic arrays, which convert solar energy into electrical energy, has steadily increased. The power generating capabilities of photovoltaic cells and photovoltaic arrays rely heavily on ambient conditions. In particular, the amount of solar radiation incident on the photovoltaic cells and photovoltaic arrays, which varies as a function of weather, clouds, time of year, and other meteorologic conditions, and the ambient temperature affect the amount of electrical energy that can be generated by the photovoltaic cells or photovoltaic arrays.
In a typical and common application of a photovoltaic array, the photovoltaic array is used to supply electric energy and electric power directly to a load. While this configuration is adequate for daylight operation, the photovoltaic array may cease to provide electric energy and electric power during periods of darkness or periods of reduced incident solar radiation. Similarly, a wind turbine may not generate energy during periods of little or no wind. Therefore, many photovoltaic array or wind turbine configurations include a battery that is charged by the photovoltaic array or the wind turbine during periods of incident solar radiation or sufficient wind. The energy stored in the battery can then be used to supply electric energy and electric power to a load during periods of darkness or periods of reduced incident solar radiation or wind. This in turn causes the battery to discharge. With this type of configuration, therefore, the photovoltaic array or the wind turbine and the battery act together to keep the load supplied with electric energy and electric power and the battery is alternately charged and discharged.
For a given temperature of the photovoltaic cell or photovoltaic array and a given amount of solar radiation incident on the photovoltaic cell or photovoltaic array, there is a curve relating the voltage across the photovoltaic cell or photovoltaic array with electric current flowing through the photovoltaic cell or photovoltaic array. Thus, there is a family of voltage/current curves for a given photovoltaic cell or photovoltaic array and varying weather conditions can create variations in the amount of electric power generated by the photovoltaic cells and photovoltaic arrays. The amount of power available from a wind turbine varies with the wind speed. In addition, ambient conditions may affect the operation and capacity of the battery.
In order to most efficiently use the electric energy and power generated by a photovoltaic cell or photovoltaic array, it is desirable to maximize the power generated by the photovoltaic cell or photovoltaic array, despite varying weather conditions. Maximizing the power generated by a photovoltaic cell or photovoltaic array requires the determination of the optimal operating conditions for the photovoltaic cell or photovoltaic array for the given weather conditions, i.e., it is necessary to find the operating point on the voltage-versus-current curve for the photovoltaic cell or photovoltaic array that maximizes the power output from the photovoltaic cell or photovoltaic array. Furthermore, a generator system incorporating a photovoltaic cell or photovoltaic array preferably is able to determine optimal operating parameters for the generator system for varying temperatures and varying amounts of solar radiation incident on the photovoltaic cell or photovoltaic array.
In addition to the problems discussed above, when a generator system is used to provide electric energy to a lighting or lamp system, additional precautions are necessary to ensure proper and continued operation of the lighting system. For example, AC lighting lamps are prone to premature failure if some amount of DC current is injected into them during operation. This problem is particularly pervasive in lighting systems using high pressure sodium, a form of high intensity discharge (HID) lamp. Fixtures, ballasts, and lamps are widely available to be powered from AC power sources. The design of a DC ballast to run an HID lamp is difficult because of the need for a high voltage starting circuit, and each DC ballast design may only be used to power one lamp type and size, requiring a family of DC ballasts to power a family of lamp types and sizes. Therefore, the generator system preferably prevents DC current from becoming a part of the input signal to the lighting system. In addition, storage batteries used in lighting systems are often not properly protected against excessive deep discharge. As a result, if the storage batteries operate for a long period of time at a low state of charge, or if the storage batteries are frequently excessively discharged, the storage batteries will often prematurely fail and, at the very least, will not maintain their peak storage capacity.
Consequently, in spite of the well-developed state of battery charging, there is still a need for relatively simple and low cost system for supplying energy and power to a battery and to a load, particularly where the load is a lighting or lamp system.